The present invention relates to a high current electrical switching device with a mechanical interlock, and in particular, to an electrical switching device with a mechanical interlock that prevents the device from being energized while a fuse access door to the device is open.
The use of equipment including industrial processors requiring relatively high currents is becoming increasingly common. In the powering of such equipment, it is considered unsafe to allow a switch to be moved to the ON position in the absence of a properly inserted plug. Attempting to insert or remove a plug from an energized receptacle, especially with a load connected to the plug, can result in arcing between the plug and receptacle with damage to the components as well as creating a substantially safety hazard to personnel. To prevent this occurrence, switches are often enclosed within a housing and commonly provided with some type of interlock mechanism.
U.S. Pat. No. 5,298,701 (Sandor) discloses a high current switch operator mounted in a closed housing having a switch and a receptacle, wherein the housing includes an interlock mechanism to prevent operation of the switch to the ON position unless a plug is properly inserted in the receptacle. A face mounted handle is attached to a shaft which directly turns a gear (designated the second gear) which carries the interlocking components.
U.S. Pat. No. 5,880,420 (Rohmer et al.) discloses a mechanical coupling between a switch, switch operator and plug interlock mechanism, whereby the switch cannot be energized unless a plug having an external key is properly inserted and releases the plug interlock mechanism.
In electrical circuits, and particularly in electrical circuits which carry high currents, it is desirable to have fuses which can protect those circuits from electrical overload. An electrical fuse is intentionally designed to be the weakest point in an electrical circuit, so that in the event of an overload, it becomes overheated to the point that it safely blows and interrupts the circuit; otherwise, overheating at some other location, such as in a building wall, may start a fire. A blown fuse is an indicator that an overload exists, perhaps because a fault has developed in the electrical supply wiring, because some inappropriate electrical device is connected to the circuit, or because an otherwise appropriate electrical device is malfunctioning. Once the cause of an overload has been identified and corrected, it is necessary to replace a blown fuse with a new one. It is desirable to have the fuses at an accessible point in a circuit, and in particular it is convenient to locate the fuses in the same housing as a switch. There is a need to provide a mechanical interlock between the switch and a door, so that fuses located in a switch housing can be readily accessed, while precluding the possibility that access be gained while the circuit is energized, and further precluding the possibility that the circuit be energized once access has been gained.
Briefly stated, a fused mechanical interlock in an electrical switching device precludes a fuse access door from being open when the switching device is energized. The fused mechanical interlock optionally cooperates with a plug interlock mechanism which prevents the switching device from being energized unless a plug is properly inserted in a receptacle.
According to an embodiment of the invention, an electrical switching device includes a housing, an electrical switch for energizing an electrical circuit when the switch is closed and de-energizing the electrical circuit when the switch is open, a fuse block connected in series with the switch, a fuse access door in the housing providing access to the fuse block but not with the switch, and a mechanical interlock operably connecting the fuse access door and the switch, and preventing the switch from being closed when the door is open, and preventing the door from being opened when the switch is closed.
According to an embodiment of the invention, an electrical switching device which has a housing includes (a) an electrical switch with an OFF and an ON position wherein the device is respectively de-energized and energized, (b) an actuation gear coupled to the switch, (copyright) at least one fuse block designed to hold a fuse in series with the switch, (d) a fuse access door in the housing which provides the only access to the fuse block, access beyond the fuse block being precluded, (e) a door catch attached to the door, (f) a lockout disposed against a spring and cooperating with the door catch, and (g) a driver bar cooperating with the actuation gear and the lockout, wherein the driver bar is slidably mounted with respect to the housing so as to be selectably displacable between an OFF and an ON position, corresponding respectively with the OFF and ON positions of the switch, the bar includes a notch which aligns with the lockout when the bar is in the OFF position such that if the door is open the spring can urge the lockout upward so that a portion thereof engages with the notch, precluding the bar from moving to the ON position until the door is closed, and the bar further including a hooked portion so that when the bar is in the ON position and the door is closed, the hooked portion engages with the door catch and precludes the door from being opened.